The Role of Interoceptive Sensitivity in Central Sensitization Symptom Severity in Fibromyalgia

Fibromyalgia is characterized by a complex symptom profile that includes pain, fatigue, sleep disturbances, and psychological distress. Interoception refers to the perception and interpretation of internal bodily signals and may be relevant to how individuals with fibromyalgia experience their symptoms. Examining interoceptive sensitivity alongside central sensitization-related symptoms may help clarify the relationship between internal bodily perception and symptom burden.

This cross-sectional observational study aims to investigate the association between interoceptive sensitivity and central sensitization symptom severity in individuals with fibromyalgia. Additional objectives are to examine the associations of interoceptive sensitivity with pain severity, fatigue, sleep quality, anxiety, and depression. Participants will undergo assessments of these domains using standardized measures, and the relationships between assessment scores will be analyzed.

The study will explore whether differences in interoceptive sensitivity are associated with central sensitization symptom burden and other clinical features of fibromyalgia. The findings may support a more comprehensive understanding of symptom experience in fibromyalgia and provide a basis for future longitudinal and interventional research.

• Central Sensitization Inventory (Other), also known as CSI: The Central Sensitization Inventory is used by some researchers to investigate pain sensitivity through symptoms associated with central sensitization and related comorbidities. It can help determine the severity of central sensitization. The scale was developed to detect central sensitization in patients with chronic pain and consists of two sections: Section A and Section B. For scoring purposes, only Section A is used. A score of 40 or higher out of 100 is associated with an increased likelihood of central sensitization.
• The Multidimensional Assessment of Interoceptive Awareness scale-2 (Other), also known as MAIA-2: The Multidimensional Assessment of Interoceptive Awareness (MAIA) 2 is a 32-item self-report questionnaire assessing eight dimensions of interoceptive awareness. Items are rated from 0 (never) to 5 (always). Each subscale score is calculated as the mean of its items, with higher scores indicating greater awareness in the corresponding dimension. No total score is calculated.
• Revised Fibromyalgia Impact Questionnaire (Other), also known as R-FIQ: The Revised Fibromyalgia Impact Questionnaire is composed of 10 items. The first item contains 11 questions related to physical functioning - each question is rated on a 4 point Likert type scale. Items 2 and 3 ask the patient to mark the number of days they felt well and the number of days they were unable to work (including housework) because of fibromyalgia symptoms. Items 4 through 10 are horizontal linear scales marked in 10 increments on which the patient rates work difficulty, pain, fatigue, morning tiredness, stiffness, anxiety and depression. The maximum scale score is 100, with higher scores associated with increasing disability.
• Numeric rating scale (Other), also known as NRS: Numeric Rating Scale will be used to determine pain intensity during assessments. Participants will be asked to rate their pain intensity by selecting a value between 0 and 10. Higher scores are associated with increased pain severity.
• Hospital Anxiety and Depression Scale (Other), also known as HADS: This scale is used to assess anxiety and depression symptoms and consists of 14 items (7 items for anxiety, 7 items for depression). For each subscale, scores range from 0 to 21: • 0-7 points: No symptoms or very mild symptoms • 8-10 points: Moderate symptoms • 11 points or higher

Primary outcomes

• Multidimensional Assessment of Interoceptive Awareness-2, MAIA-2 [baseline]: The participant is required to evaluate "how often each statement generally applies to you in daily life" using a six-point Likert scale with 32 items, where responses range from 0 ("never") to 5 ("always"). The score for each scale is calculated by averaging the scores of its items (ranging from 0 to 5), with higher scores indicating a higher expression of the internal perception components examined by the survey.

Secondary outcomes

• Central Sensitization Inventory, CSI [Baseline]: The central sensitization scale is a tool used to assess the hypersensitivity of the central nervous system. This scale includes questions that examine individuals' pain perception and its effects on daily life to detect the effects of central sensitization, which are often seen in chronic pain conditions. The scale evaluates how individuals perceive pain in response to physical contact or other stimuli (pain sensitivity), changes in their sensitivity to hot, cold, or pressure (sensory changes), how the persistence of pain affects their daily activities, and the impact of pain on their emotional state (anxiety, depression, etc.).
• Revised Fibromyalgia Impact Questionnaire [Baseline]: It will be used to evaluate the disease impact and symptom severity related to fibromyalgia in participants. It is a scale that evaluates the functional status, overall disease impact, and symptom severity in fibromyalgia patients over the past 7 days. As the total score obtained increases, it is accepted that the disease impact associated with fibromyalgia also increases.
• HOSPITAL ANXIETY AND DEPRESSION SCALE [Baseline]: It is a 14-item self-report scale that quickly, reliably, and independently of medical conditions assesses patients' anxiety and depression symptoms over the past week.
• Numeric Pain Rating Scale, NPRS [Baseline]: Pain severity will be evaluated using a scale ranging from 0 (no pain) to 10 (unbearable pain). Participants will be asked to rate their average pain levels over the past week.
• Fatigue Severity Scale [Baseline]: It will be used to assess the participants' level of fatigue. The scale is a 9-item measure that evaluates the impact of fatigue on daily life activities, physical function, motivation, and social life. The items are scored on a scale of 1-7, with higher scores indicating greater fatigue severity.
• Pittsburgh Sleep Quality Index [Baseline]: It will be used to evaluate the sleep quality of the participants. It is a scale that evaluates sleep quality and sleep disorders within the last month. The scale consists of seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The total score ranges from 0 to 21, with higher scores indicating worse sleep quality.

Sex: Female, ages: 18 Years to 65 Years

Inclusion Criteria:

* Women patients aged 18-65
* Diagnosed with fibromyalgia according to the 2016 ACR criteria
* Experiencing widespread pain for at least 3 months
* Having the cognitive ability to complete the scales
* Having read and signed the informed consent form (ICF)

Exclusion Criteria:

* Being under 18 or over 65 years old
* Pregnancy
* Active inflammatory rheumatic disease
* Neurological disease
* Malignancy
* Severe psychiatric disorder
* Serious systemic disease such as heart or kidney failure

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• Feyza Nur Yücel, Assoc. Prof., Study chair, Saglik Bilimleri Universitesi